The invention concerns a method of regenerating the duration of pulses of random duration which are emitted by the automatic switching units of an automatic telephone network in analog communication systems. Such pulses modulate on an off-off basis a sinusoidal carrier whose frequency is outside the speech frequency range such as described in C.C.I.T.T. R2 for example. The pulse modulated carrier passes through narrow-band signal filters both at the signal transmitter and receiver which will cause deformations of the steep leading and trailing edges of the pulses. At the signal receiver, the input level of the signal may vary by a number of decibels on either side of the rated value, and this prevents any regeneration based on the signal level from being accurate if no special care is taken.
Devices have already been disclosed to regenerate signalling pulses. For example, French Pat. No. 2,094,739, applied for on the July 30, 1970, by the Societe Anonyme de Telecommunications, describes a method and the corresponding apparatus by which the signalling pulse can be transformed after detection into a pulse having steeper edges. The leading edge appears at the instant when the leading edge of the received signalling pulse reaches a preset value V.sub.o, and the trailing edge appears at the instant at which the trailing edge of the pulse received reaches a value V.sub.o ' which is substantially proportional to its peak voltage. By this method, it is possible to reduce the distortion of the duration of the pulse when its level varies. This device supplies a pulse in which the duration of the edges is a function of that of the edges of the input signal. When testing whether the signalling regenerator is operating satisfactorily, it is not possible to replace an input signal pulse by a slowly varying unidirectional voltage without producing an excessive energy dissipation in the retransmitter. Furthermore integration of this regenerator seems difficult.